Mycobacterium tuberculosis is the bacterium that causes most cases of tuberculosis (TB). When in the lungs, M. tuberculosis is taken up by alveolar macrophages, but they are unable to digest the bacteria. The cell wall prevents the fusion of the phagosome with a lysosome. The bacteria multiply unchecked within the macrophage. The bacteria also evade macrophage killing by neutralizing reactive nitrogen intermediates.
TB is a common and often deadly infectious disease that usually attacks the lungs (as pulmonary TB), but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, the gastrointestinal system, bones, joints, and even the skin. Other mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti, and Mycobacterium microti also cause tuberculosis, but these species are less common.
The typical symptoms of tuberculosis are a chronic cough with blood-tinged sputum, fever, night sweats and weight loss. Infection of other organs can cause a wide range of symptoms. The diagnosis relies on radiology (commonly chest X-rays), a tuberculin skin test, blood tests, as well as microscopic examination and microbiological culture of bodily fluids. Tuberculosis treatment is difficult and requires long courses of multiple antibiotics. Contacts are also screened and treated if necessary.
One third of the world's current population has been infected with M. tuberculosis, and new infections occur at a rate of one per second. About one in ten of these latent infections will eventually progress to active disease, which, if left untreated, kills more than half of its victims.